Species Distribution Model for the Asian Tapir and Vegetation Characteristics of Batang Gadis National Park, North Sumatra, Indonesia

The Asian tapir is a primitive mammal whose habitat is heavily fragmented due to human activities. Studies on the Asian tapirs in Sumatra are very few, thereby basic information for developing tapir conservation programmes is limited. This study aimed to develop the species distribution model to map the potential distribution of tapirs in Batang Gadis National Park (BGNP), investigate the characteristic of tapir habitat, and identify tapir feed plants around BGNP. The model was developed using the Maximum Entropy (Maxent) approach, based on the existing information on tapir occurrence in BGNP and environmental variables. Vegetation characteristics in different land cover (primary forests, secondary forests, and open fields) were investigated using the strip transect method. This study found that zonal classification, temperature and precipitation have the greatest percentage contribution to the model. The model estimated that around 24.45% of BGNP areas are suitable for tapir habitat, and tapirs distribute near community gardens. Our results also showed that plant diversity at study sites was categorised as moderate-high. About 23 plant species dominated by the Moraceae family were identified as feed plants for tapirs. In developing tapir conservation programmes, BGNP management needs to consider tapir distribution that is closed to community gardens. We propose BGNP to enrich feed plants in open fields of the wilderness and traditional zones; reduce the canopy cover in the wilderness and utilisation zones to stimulate the growth of feed plants; facilitate local people to live harmoniously with tapirs; involve local communities in tapir conservation programmes; encourage local communities to plant non-palatable crops for tapirs; and provide a compensation scheme.


INTRODUCTION
Tapirs, the most primitive large-bodied mammal, have inhabited tropical forests since the Pleistocene period (Samantha et al. 2020).The Asian tapir (Tapirus indicus) is one of the four remaining species of tapirs distributed in several countries of Southeast Asia such as Indonesia, Laos, Malaysia, Myanmar, Thailand and Vietnam (Novarino 2005;O'farrill et al. 2013).In Indonesia, tapirs can be found in almost all provinces of Sumatra Island (Holden et al. 2003;Marlius et al. 2018).Tapirs are known as solitary and nocturnal animals (Marlius et al. 2018).Tapirs have important ecological roles as seed dispersers and seed predators (Cranbrook & Piper 2009;Wittayarat et al. 2021).The seed dispersed by tapirs may grow and facilitate carbon sequestration (Paolocci et al. 2019).
In recent decades, the population of tapirs declined dramatically due to habitat destruction, poaching, road construction, and global warming (Meyer et al. 2022;Samantha et al. 2020).The remaining tapir population in nature is below 2,500 individuals, and it is projected to decrease by 20% in 2040 (Wittayarat et al. 2021).The Asian tapir is currently classified as an endangered species by the International Union for Conservation of Nature (IUCN) and listed in Appendix A of the Convention on International Trade in Endangered Species (CITES) (Traeholt et al. 2016).In Indonesia, the Asian tapir has been protected since 1931 (Holden et al. 2003).
Batang Gadis National Park (BGNP) is one of the most important tapir habitats on Sumatra Island.Kuswanda and Mukhtar (2010) found that the density of tapirs in this national park is about 0.09 individuals/ha.Meanwhile, Linkie et al. (2013) noted a high probability of occurrence of tapirs in this national park (0.90 ± 0.06).However, some concerns about the existence of tapirs in BGNP still exist, notably due to the land use change and habitat destruction.In 2012, about 30% of BGNP was excised for gold mining (Linkie et al. 2013).Studies related to tapirs in Sumatra, especially in BGNP, are still limited.This condition has some consequences for the establishment of tapir conservation programmes in BGNP.Schank et al. (2015) pointed out that the species distribution model is the foundation to understand the ecology, conservation, and management strategies of a species.Currently, this model has been developed for various purposes, especially for conservation management.The species distribution model quantifies the probability of species distribution in certain areas and times using environmental variables (Franklin 2010).This model is generally known as species distribution modeling (SDM) and is described formally as Niche modeling, habitat modeling, habitat suitability modelling, and predictive habitat distribution modelling (Miller 2010).The most common approach used to develop SDM is maximum entropy (Maxent).Maxent models suitable environmental conditions of a species based on species occurrences data and a set of environmental variables (Phillips et al. 2006).Maxent is generally easy to use and efficient to identify suitable areas for a species (Clements et al. 2012;Cordeiro et al. 2016;Merow et al. 2013).Currently, SDM for tapir has been developed in other parts of the world, e.g., South America, Ecuador, Peninsular Malaysia and Peru (Cordeiro et al. 2016;More et al. 2022;Ortega-Andrade et al. 2015).However, this model is not developed yet for tapirs in BGNP.
The main objective of this study is to: 1. Develop the species distribution model to provide the potential distribution map of tapirs in BGNP. 2. Investigate the characteristic of tapir habitat.

Identify tapir feed plants around BGNP.
This study is expected to provide important information for tapir conservation programmes in BGNP.

Study Site
This study was conducted in BGNP in Mandailing Natal (Madina) Regency (Fig. 1).Batang Gadis was designated as a national park on 29 April 2004 by the decree of the Minister of Forestry No: SK.126/Menhut-II/2004 on 29 April 2014 (Ministry of Forestry 2004).The BGNP originally covered about 108,000 ha of forests in the District of Mandailing Natal (Madina), North Sumatra Province.In 2012, the total area of the BGNP shrank to 72,804 ha (Decree of the Minister of Forestry: SK.3973/Menhut-VII/KUH/2014) (Ministry of Forestry 2014).The BGNP covers 10 districts and 32 villages.The BGNP comprises five zones, three management units, and eight resorts (Balai Taman Nasional Batang Gadis 2020).

SDM development
Maxent uses several data inputs (spatial data with the same resolution and extent) to quantify the potential distribution of tapirs in BGNP.About 25 tapir occurrences derived from the Spatial Monitoring and Reporting Tool (SMART) patrol system in BGNP were used as data inputs to develop the model.The SMART patrol system is a tool developed to measure, evaluate, and improve monitoring in conservation areas (Sadikin et al. 2016).Environmental variables (Table 1) were used as the main predictors.The elevation data were collected from the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM).The elevation map was created from the GDEM using ArcMap version 10.The slope was calculated from the Digital Elevation Model (DEM) (Austin 2007;Saputra & Lee 2021).
Climate data were collected from the WorldClim dataset that is providing several bioclimatic predictors for supporting ecological applications (O'Donnell & Ignizio 2012).The bioclimatic predictors used to develop the model are provided in Table 2.During the first run, we found that Bio 4, Bio 7 and Bio 15 did not have significant contributions to the model.Therefore, they are excluded from the final model.
BGNP was divided into five zones: core zone, specific zone, utility zone, wilderness zone and traditional zone (Balai Taman Nasional Batang Gadis 2020) (Table 3).Land cover data were derived from satellite images in 2020.The land cover classification was modified from the Ministry of Environment and Forestry Land Use Land Cover Map Classification.In this study, the land cover in BGNP was classified into crops, forests, open areas, residential areas and shrubs (Table 4).

The characteristic of the tapir habitat
The investigation of the characteristic of tapir habitat and tapir feed plants was performed in Pagar Gunung Resort (Resort IV), Sopotinjak Resort (Resort VII), and their supporting villages between March and October 2021 (Fig. 1).Pagar Gunung and Sopotinjak Resorts are located at altitudes of 1,400 m and 1,200 m, respectively.Prabuningrum (2020) noted that these resorts are the main habitat for tapir in the BGNP.
Tapir habitat and feed identification were conducted in three different land covers: primary forests (PFs), secondary forests (SFs) and open fields (OFs) (Fig. 2).This study was performed in the spot which was detected by camera traps as tapir habitat (Fig. 3), or spots where tapir footmarks or faeces were observed during the study.Vegetation analysis was performed using the strip transect method with systematic random sampling.A 1.6 km line transect was installed in each land cover.Nested plots (2 × 2 m 2 and 5 × 5 m 2 plots) were then installed along the transect to record seedling and understory and sapling, respectively.The distance between plots was about 40 m (Alatar et al. 2012).Vegetation analysis was confined to the sapling, seedling and understory as tapirs just used vegetation at these growth stages for food (Meyer et al. 2022;O'farrill et al. 2013;Santiapillai & Ramono 1990).The sapling is categorised as a plant with a stem circumference between 6.3 cm and 31.4 cm.The seedling is a plant with a stem circumference of less than 6.3 cm and/or heights of less than 1.5 m.The understory is a non-woody plant e.g., grass, shrubs and herbs (Fachrul 2007).Tapir feed plants were recorded during the vegetation analysis.Feed plants identification was performed by BGNP officers and local people who had a good knowledge of tapirs.

SDM for tapir
The spatial analysis was performed to provide a suitable area for tapir distribution across the BGNP.The data of tapir occurrence and environmental variables were converted into spatial data with the same extent and resolution to produce better results in the Maxent model.The resolution used in this study is 30 m.The coordinates for the data raster were extended to 0.45°N-1.02°Nand 99.24°E -99.8°E.
The spatial analysis was conducted to produce a tapir potential distribution map.The probability of tapir distribution is arranged from 0 to 1, where a higher probability number indicates a higher probability of tapir distribution (Loi 2008).The probability threshold for an area classified as suitable for tapir distribution is greater than 0.4.The probability distribution < 0.4 was classified as an unsuitable area for tapir distribution.
The model was validated using the receiver operating characteristic (ROC) curve.The ROC curve analyses the performance of a model at all classification thresholds (Phillips et al. 2004).The quality of the model is determined by the Area 64 Under Curve (AUC) values (Phillips et al. 2006).The higher the AUC values, the better the quality of the model is.A good model should have AUC values above 0.5 (Elith et al. 2006).

Tapir habitat characteristic analysis
The characteristics of vegetation were analysed using the species diversity index referring to the Shannon and Weaver equation (Shannon 1948) and the Hill index (Geng et al. 2019).Plant composition was analysed using the important value index (IVI) equation (Fachrul 2007;Tabares et al. 2018).The relationship between vegetation characteristics and plants consumed by the tapir was analysed using percentage analysis and Chi-square analysis with the Statistical Package for Social Science (SPSS) 23.0 software for Windows (IBM Corp. SPSS Statistics; Somers, NY, USA).

SDM for Tapir in BGNP
Our modelling estimated an AUC of 0.869, indicating a good validity and reliability of the model to predict the distribution of tapirs in BGNP (Hijmans & Elith 2013;Phillips et al. 2006).The binary map estimated that 24.45% of the BGNP area is suitable for tapir habitat (Fig. 4).The model also showed that tapir habitats are generally near the border of BGNP.This finding is slightly identical to Schank et al. (2015) who modelled that only 27.2% of tapir suitable habitat across the Mesoamerican countries (except El Salvador) is in protected forests.In general, tapir habitats comprise PFs, SFs, mixed forests, rubber and oil palm plantations, community lands, and locations around human settlements (Gemita et al. 2007).
Among variables used to develop the model, zonal classification and bioclimatic factors (Bio 4 and Bio 13) have higher contributions to the model.This finding is identical to Schank et al. (2015) who also found that temperature and precipitation are variables with the greatest percentage contribution to the species distribution model for tapir across the Mesoamerican countries.According to Oliveira-Santos et al. (2010), temperature and rainfall are among the important variables for tapirs to select their habitats.

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Temperature seasonality (Bio 4) contributed 36.5% to the model.The model revealed that tapirs can be found in an area with a temperature around 32°C-7°C (the probability is greater than 0.4) (Fig. 5).The model also showed that the probability of tapir occurrence in BGNP will be lower when the temperature is above 37 o C or less than 32°C.This finding is in contrast with Clements et al.
(2012) who found a lower probability of tapir occurrence in Peninsular Malaysia in the range of temperatures greater than 25°C-26°C.
Association of Zoos and Aquariums (AZA) Tapir TAG (2013) pointed out that tapirs are heat tolerant that can tolerate temperatures up to 38°C.However, to maintain the thermal and water balance, tapirs alter their activity by becoming more nocturnal during the hotter days and diurnal during the colder days or select shaded and humid environments (Oliveira-Santos et al. 2010).
About 32.7% of the tapir distribution model in BGNP is explained by the zonal classification.Our modelling predicted the highest probability of tapir occurrence in the wilderness zone and a small part of the traditional zone (Fig. 6).Most of the wilderness and traditional zones adjacent to the buffer zone were used to be community gardens before being designated as a national park (Kuswanda & Antoko 2008).During our observation, these gardens have become OFs grown by numerous plants including tapir feeds plants.This condition is assumed to be one of the main drivers for tapirs to distribute in the wilderness and traditional zones.Precipitation of the wettest month (Bio 13), which contributed 10.2% to the model, estimated a higher probability of tapir occurrence in the range of precipitation of 320 mm/month-370 mm/month and more than 470 mm/month (Fig. 7A).BGNP topographical conditions are ranging from lowlands to mountains.Different latitudes are expected to have different precipitations.The model also predicted that tapirs can be found in an area with the precipitations of 370 mm/month-470 mm/month, though the probability of occurrence is relatively low (Fig. 7B).Oliveira-Santos et al. (2010) pointed out that high rate of precipitation lead tapirs to be active throughout the day, to keep the thermal balance.

Land use change in BGNP
Forest conversion may lead to habitat destruction and fragmentation, thereby threatening wildlife, including tapirs (Corlett 2007;Davis et al. 2013;Noga et al. 2018).Human activities in forests and hunting activities might also bring negative effects on wildlife, especially tapirs, as they reduce the active hours of tapirs and decrease the tapir population (Marlius et al. 2018;Ripple et al. 2016).Therefore, habitat monitoring is important in conserving tapirs.
This study found that forests in BGNP declined by more than 2.97% between 2000 to 2010 (Table 5).Surprisingly, from 2010 to 2020, forest covers increased by 3.07%, indicating crops and shrubs conversion into forests (Table 5).Note: The change reveals the increase or the decrease of a land cover in a certain period.The "+" and "-"signs represent the increase and the decrease of the land cover, respectively.

Species diversity and vegetation composition in BGNP
This study found that land cover changes had a great impact on the characteristics of vegetation in BGNP.This finding is in accordance with previous studies stating that vegetation characteristics are highly affected by the land cover (Alikodra 2019;Borisade et al. 2021;Garizábal-Carmona & Mancera-Rodríguez 2021).Except for sapling in Sopotinjak OFs, the density and frequency of vegetation at various growth levels in SFs and OFs were higher than those of PFs (Table 6).Forest cover loss has allowed the sunlight to penetrate the forest floor and attracted pioneer species to grow (Dupuy & Chazdon 2008;Kuswanda & Mukhtar 2010).In PFs, only a certain species could adapt to high humidity, low temperature and wet forest floors (Fachrul 2007;Luo et al. 2021).
H' of the vegetation at different growth stages in Pagar Gunung and Sopotinjak Resorts were classified as medium (2 ≤ H' < 3) and high (H' ≥ 3), respectively (Barbour et al. 1987).H' of the seedling and understory in SFs and OFs is higher than PFs (Table 6).H' of the sapling in Pagar Gunung SFs was higher than PFs.In Sopotinjak, H' of the sapling for OFs was lower than that of PFs.In general, the H' of seedling, understory, and sapling in all land covers was higher than those of natural forests in the Tesso Nillo National Park (TNNP).Kusumo et al. (2016) reported that the H' of the seedling and sapling in natural forests of the TNNP were only about 2.18 and 2.05, respectively.
This study also indicates that the characteristics of vegetation are influenced by elevation.Species density and H' of PFs in Sopotinjak (1,200 m) were higher than those of Pagar Gunung (1,400 m).Different elevations may have different weathers and microclimates that may affect species composition (Lu et al. 2021).This condition may also influence habitat carrying capacity, wildlife distribution, activities, and even its metabolic processes (Fuller et al. 2019;Kuswanda et al. 2021).Notes: D = density; F = frequency, H'= h-index (the Shannon-Wiener diversity index); N = the abundance index.

Important Value Index (IVI)
The IVI is a parameter used to measure the ecological significance of a species in a community or a site (Yuningsih et al. 2021).The number of plant species recorded in Pagar Gunung and Sopotinjak Resorts at the seedling, understory and sapling stages was 94.Pagar Gunung was occupied by 60 plant species (31 species in PFs and 39 species in SFs).In the seedling and understory stages, PFs and SFs were dominated by R. teysmannii and Syzygium sp., respectively (Table 7).In the sapling stage, PFs and SFs were dominated by H. buruensis and P. obovatum, respectively.The total plant species in Sopotinjak was 75 (44 species in PFs and 43 species in OFs).PFs in Sopotinjak were dominated by H. buruensis (seedling and understory) and L. brachystachys (sapling).Meanwhile, OFs were dominated by L. hexandra (seedling and understory) and P. sarmentosum (sapling) (Table 7).Sambas et al. (2018) pointed out that the species with the highest IVI will become important species in the vegetation in the future.

Tapir Feed Plants
Tapirs are selective browsers that choose high-quality plants for their feed (Gearty 2012).Tapirs spend most of their time foraging (Naranjo 2009).They forage in their home ranges and will return to the same location within 90 to 100 days (Maharani et al. 2019).Tapirs generally consume soft, fresh and easily chewed young leaves, fruits and new growth twigs (Holden et al. 2003;Williams & Petrides 1980).They also consume grasses and pioneer species, including Artocarpus sp.(Moraceae).
In total, tapirs feed on at least 380 plant species (Simpson et al. 2013).
During this study, about 23 feed plant species (14 families) were identified in Pagar Gunung and Sopotinjak Resorts (see Appendix).These feeds are dominated by the Moraceae family.These feeds were generally consumed for their leaves (Fig. 8).About 34% of the feeds were also consumed for their fruits.About 26.1% of feeds, e.g., Artocarpus elasticus, Ficus toxicaria and Pouzolzia zeylanica, were consumed entirely by tapirs.This finding is identical to Tobler et al. (2006) who also found that the dominant plant parts consumed by tapirs are leaves.In general, the number of leaves eaten by tapirs varies between feed plant species (Simpson et al. 2013).Tapirs prefer nitrogen-fixing species (Downer 2001).The daily feed consumption of tapirs is about 4%-5% of its body weight (Gearty 2012).The proportion of feed plants to the total vegetation in Pagar Gunung and Sopotinjak Resorts was less than 40%.The density, diversity and abundance of feed plants at the seedling, understory and sapling stages in OFs and SFs were higher than in PFs (Fig. 9).The high density, diversity and abundance of feed in SFs and OFs may attract the tapir to browse feed in SFs and OFs.In general, tapirs prefer to forage in SFs because SFs are grown with numerous young plants stimulated by sunlight penetration on the forest floor (Samantha et al. 2020;Schank et al. 2020;Tobler 2002).Moreover, feeds grown in SFs have high concentrations of proteins and nutrients in their buds and leaves (Salas & Fuller 1996).A chi-square analysis revealed that the asymp.sig.(2-sided) value was 0.245 (> 0.05), indicating there is no relationship between vegetation characteristics and tapir feed plants in each type of land cover for various growth stages.This finding is identical to Salas and Fuller (1996) who also found that there was no relationship between the abundance of plant species and the abundance of tapir feed plants in Tabaro River valley, Southern Venezuela.

Implications for Tapir Conservation Programmes
Tapirs require a huge area for foraging (Marlius et al. 2018).Tapirs generally prefer a highly vegetated habitat with a dense canopy cover, lots of food and water, and far from roads (Samantha et al. 2020).This study clearly showed that the tapir habitat in BGNP is still in good condition with low forest disturbances in the last 10 years.The tapir habitat in BGNP was also occupied by various plants that can be used as food for tapirs.However, concerns should be given to the distribution of tapirs in BGNP.The model showed that tapirs distribute near the traditional zone where community crops are growing.This condition may attract tapirs to enter the gardens, destroy the crops and generate human-tapir conflicts.Previous studies have shown that tapirs prefer to consume community crops, e.g., young bean shoots, corn, cabbage, pineapple, potatoes and watermelon (Novarino 2005;Suárez & Lizcano 2002;Waters 2015).Local people also stated that tapirs also prefer to consume coffee and pumpkin planted by local people in BGNP.
Our interview with local communities revealed that tapir foot marks were frequently observed in the garden, indicating that tapirs in BGNP have started to invade the community garden.At this stage, local people still have a good perception of tapirs, and there are no records of human-tapir conflicts or tapirs hunting in BGNP surrounding villages.When conflict intensity is escalating, however, people's perceptions and attitudes toward tapirs may change, and human-tapir conflicts may occur in this national park.
This issue is needed to consider by the BGNP management in managing tapir conservation programmes.Without management intervention, human-tapir conflict may occur, and the population of tapir in BGNP will continue to decline, as experienced by the Tapanuli orangutan (Kuswanda et al. 2021).
We suggest the BGNP management to perform the following strategies: 1. Enriching OFs of wilderness and traditional zones with feed plants which are not utilised by local communities, such as Artocarpus elasticus, Ficus toxicaria, Mikania scandens, Hemigraphis buruensis and Zingiber sp.
2. Trimming the tree crown in the wilderness and utilisation zones to accelerate the growth of feed plants on the forest floor.
3. Providing education, training and guidance for local people to live harmoniously with tapirs.
4. Involving local community in tapir conservation programmes.
5. Encouraging community to grow non-palatable crops for tapirs.
6. Providing compensation scheme for local people affected by tapirs.

CONCLUSION
The most important variables in developing the species distribution model for tapir in BGNP are zonal classification, temperature and precipitation.Our modelling reveals that 24.45% of BGNP areas are suitable for tapir habitat.We also found that tapir habitat conditions in BGNP are still in a good condition where forest conversion was absent in the last 10 years.About 23 feed plant species dominated by the Moraceae family were identified in Pagar Gunung and Sopotinjak Resorts.These feeds were predominantly consumed for their leaves.About 34% of feeds were also consumed for their fruits, and 26.1% of the feeds were consumed entirely by the tapir.The model also shows that tapirs distribute near the traditional zone where the community garden is located.This condition may attract tapirs to have close contact with humans, and lead to human-tapir conflicts.BGNP management needs to consider this finding in developing tapir conservation programmes in BGNP.Several strategies proposed to overcome this issue are planting feed plants in Ofs, e.g., the wilderness and traditional zones; reducing the canopy cover in the wilderness and utilisation zones to enhance the growth of feed plants; educating, training and guiding local people to live harmoniously with tapirs; engaging the community in tapir conservation programmes; suggesting the community to cultivate non-preferred crops by tapirs; and providing compensation scheme for farmers disturbed by tapirs.

Figure 2 :
Figure 2: General pictures of land cover in study sites: (A) PFs in Sopotinjak Resort; (B) OFs in Sopotinjak Resort; (C) PFs in Pagar Gunung Resort; and (D) SFs in Pagar Gunung Resort.

Figure 3 :
Figure 3: The spots identified as tapir habitat through (A) camera traps; (B) faeces; and (C) foot marks (Source: Taman Nasional Batang Gadis and this study).

Figure 5 :
Figure 5: Response of tapir distribution model to the temperature seasonality.

Figure 6 :
Figure 6: The tapir potential distribution model according to the zone in BGNP.

Figure 7 :
Figure 7: (A) Response of tapir distribution model to Bio 13; and (B) tapir potential distribution model based on precipitation.

Figure 8 :
Figure 8: The percentage of plant parts consumed by tapir.

Figure 9 :
Figure 9: The characteristic of feeds in different resorts and growth stages.

Table 1 :
Environmental variables used to develop SDM for tapir in BGNP.

Table 2 :
Bioclimatic predictors used in developing species distribution model for tapir in BGNP.

Table 4 :
Land cover classification in BGNP.

Table 5 :
Land-cover change in BGNP from 1990 to 2020.

Table 6 :
The density and diversity of vegetation around the tapir habitat in BGNP.

Table 7 :
Top three dominant species in different land cover in different resorts.
Notes: RD = Relative Density, RF = Relative Frequency